The opening of fibers is a process consisting of progressively imposing a common longitudinal orientation to an aggregation of textile fibers which are fed as non-organized flocks, for obtaining, as a result, so-called fiber webs.
Examples of such machines for opening fibers are carding machines.
Carding machines comprise cylinders, the lateral wall of which is externally provided with clothings made, for instance, of continuous metal wires having a saw-tooth profile, said wires being wound to form spaced spirals or coils. In the carding process, the fibers to be carded are simultaneously “engaged” by clothings of two different drums or cylinders having different speeds and/or different directions of rotation.
The carding process involves the sliding of the fibers with friction onto the metal profile of the clothings of said drums or cylinders, with consequent generation of heat.
In recent years, carding machines have undergone remarkable technical improvements, which have brought to a progressive increase of their performances in terms of the quantity of fibers treated in unit time and quality of the finished products.
In particular, the increase of the quantity of fibers treated in unit time involves an increased carding action, with a consequent increase of the above-mentioned friction and the inherent production of heat in the areas where the fibers are carded.
The remarkable increase of heat development in the carding machines of the latest generations, determines, though to a different amount depending on the kind of fibers being treated, the following negative effects:
accelerated evaporation of the water which is normally added to the fibers in the treatments upstream of the carding machines, to permit correct carding; an increase of the percentage of water added upstream, for compensating the heavier evaporation is not possible, since it would involve further technical problems of another nature; and
the achievement of operational temperatures which are close to the glass transition point or the melting point of the fibers; approaching these points involves a downgrading of the physical characteristics of the fibers and of the mechanical properties thereof (breaking load, traction strength, resiliency, and so on).
The above-mentioned negative effects act against, and therefore involve a limitation to, the possibility of working the fibers in the very large quantities desired, with the high quality standards required for the finished products.